1. Field of the Invention
This invention generally relates to decision support systems. More specifically, the invention relates to decision support systems designed for managing applications and resources using rule-based constraints in scalable mission-critical clustering environments.
2. Prior Art
A cluster is a collection of resources (such as nodes, disks, adapters, databases, etc.) that collectively provide scalable services to end users and to their applications while maintaining a consistent, uniform, and single system view of the cluster services. By design, a cluster is supposed to provide a single point of control for cluster administrators and at the same time it is supposed to facilitate addition, removal, or replacement of individual resources without significantly affecting the services provided by the entire system. On one side, a cluster has a set of distributed, heterogeneous physical resources and, on the other side, it projects a seamless set of services that are supposed to have a look and feel (in terms of scheduling, fault tolerance, etc.) of services provided by a single large virtual resource. Obviously, this implies some form of continuous coordination and mapping of the physical distributed resources and their services onto a set of virtual resources and their services.
Typically, such coordination and mappings are handled by the resource management facilities, with the bulk of the work done manually by the cluster administrators. Despite the advances in distributed operating systems and middleware technology, the cluster management is highly human administrator bound (and hence expensive, error-prone, and non scalable beyond a certain cluster size). Primary reasons for such a state-of-the-art is that existing resource management systems adopt a static resource-centric view where the physical resources in the cluster are considered to be static entities, that are either available or not available and are managed using predetermined strategies.
These strategies are applied to provide reliable system-wide services, in the presence of highly dynamic conditions such as variable load, faults, application failures, and so on. The coordination and mapping using such an approach is too complex and tedious to make it amenable to any form of automation.
Application management middleware has traditionally been used for products that provide high availability such as IBM's HA/CMP and Microsoft's Cluster Services (MSCS). HA/CMP's application management requires cluster resource configuration. Custom recovery scripts that are programmed separately for each cluster installation are needed. Making changes to the recovery scheme or to basic set of resource in the cluster requires these scripts to be re-programmed. Finally, HA/CMP recovery programs are stored and executed synchronously on all nodes of the cluster. MSCS provides a GUI-driven application manager across a two-node cluster with a single shared resource: a shared disk [see, M. Sportack, Windows NT Clustering BluePrints, SAMS Publishing, Indianapolis, Ind. 46290, 1997].
These two nodes are configured as a primary node and a backup node; the backup node is used normally pure backup node and no service-oriented processing is performed on it. Configuration and resource management is simplified with MSCS: there is only one resource to manage with limited management capabilities.
Tivoli offers an Application Management Specification (AMS) mechanism, which provides an ability to define and configure applications using the Tivoli Application Response Measurement (ARM) API layer [Tivoli Corp., Tivoli and Application Management, http:/www: tivoli.com/products/documents/whitepapaers/body.map.wp.html, 1999. These applications are referred to as instrumented applications. The information gathered from the instrumented applications can be used to drive scripts by channeling the information through the Tivoli Event Console (TEC). The TEC can be configured to respond to specific application notification and initiate subsequent actions upon application feedback. The current version of ARM application monitoring is from a single system's perspective. Future versions may include correlating events among multiple systems.
Over the last few years several new efforts towards coordinating and managing services provided by heterogeneous set of resources in dynamically changing environments. The examples of these include TSpaces [see, P. Wyckoff, S. McLaughry, T. Lehman, and D. Ford, T Spaces, IBM Systems Journal, pp. 454-474, vol. 37, 1998] and the Jini Technology [see, K. Edwards, Core JINI, The Sun Microsystems Press Java Series, 1999]. The TSpaces technology provides messaging and database style repository services that can be used by other higher level services to manage and coordinate resources in a distributed environment. Jini, on the other hand, is a collection of services for dynamically acquiring and relinquishing services of other resources, for notifying availability of services, and for providing a uniform means for interacting among a heterogeneous set of resources.